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Modeling a PNP circuit in LTspice, is this a short?
Yamin:
Hi guys,
I was just messing about modeling a PNP circuit in LTspice. I made a mistake with the first circuit where I connected the second voltage supply directly to ground. I measured the current through the voltage source and the plot shows the result. Isn't the voltage source connected directly to ground? Shouldn't it show a dead short/infinite current draw?
The correct circuit is on the right.
Thanks in advance for the help.
Jay_Diddy_B:
Hi,
In this circuit the voltage across the 250 Ohm resister is
12V + 5V - Vbe = 16.3
The current is
16.3V / 250 \$\Omega\$ = 65mA
This is very close to what LTspice is giving you.
Regards,
Jay_Diddy_B
Yamin:
--- Quote from: Jay_Diddy_B on April 30, 2020, 11:50:34 pm ---Hi,
In this circuit the voltage across the 250 Ohm resister is
12V + 5V - Vbe = 16.3
The current is
16.3V / 250 \$\Omega\$ = 65mA
This is very close to what LTspice is giving you.
Regards,
Jay_Diddy_B
--- End quote ---
Thanks Jay,
I'm sorry I am finding it a bit hard to follow your calculations. Are you doing it for the loop of the circuit on the right? Hope you would elaborate this for me.
How is connecting the positive terminal directly to ground not shorting it?
Thanks so much again.
langwadt:
--- Quote from: Yamin on May 01, 2020, 12:11:17 am ---
--- Quote from: Jay_Diddy_B on April 30, 2020, 11:50:34 pm ---Hi,
In this circuit the voltage across the 250 Ohm resister is
12V + 5V - Vbe = 16.3
The current is
16.3V / 250 \$\Omega\$ = 65mA
This is very close to what LTspice is giving you.
Regards,
Jay_Diddy_B
--- End quote ---
Thanks Jay,
I'm sorry I am finding it a bit hard to follow your calculations. Are you doing it for the loop of the circuit on the right? Hope you would elaborate this for me.
How is connecting the positive terminal directly to ground not shorting it?
Thanks so much again.
--- End quote ---
to get a short you need to connect both terminals to the same thing, you have one side to ground the other to a resistor
you can flip it around and set the voltage to -5V it is the same
Jay_Diddy_B:
Maybe this will help:
There is 17V between A and B
There is 17V - VBe = 16.3 between C and B
Does that help?
Jay_Diddy_B
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